Method and system for water conservation

ABSTRACT

A method and system for water conservation relies upon the reduction of evaporative losses from water storages having a high ratio of surface area to depth. The system comprises a plurality of buoyant flexible membrane strips interconnected along adjacent edges and anchored by anchor members about the periphery of the water storage. The membrane strips include spaced apertures to prevent accumulation of rain water on upper surfaces thereof.

BACKGROUND OF INVENTION

[0001] This invention is concerned with a method and apparatus forconservation of water.

[0002] The invention is particularly concerned with the reduction ofevaporation losses from water storages having a high ratio of surfacearea to water depth.

[0003] In many regions of Australia and elsewhere in the world, thecapacity for sustainable horticulture is dependent on the availabilityof water.

[0004] In arid and semi-arid regions, a level of sustainablehorticulture has been achieved by building large but relatively shallowwater storage dams covering many hectares.

[0005] Water levels in such dams can be topped up in rainy seasons bydrainage from catchment areas where the topography is appropriate orotherwise by pumping water from creeks or rivers when water is flowingtherein.

[0006] A major disadvantage of such water storage systems is the highrate of water loss due to evaporation due to the combined effects ofwind and water surface temperature.

[0007] Evaporative losses are generally measured in megaliters/hectarewhere a 100 mm reduction in water depth per hectare equals onemegaliter.

[0008] In semi-arid areas where average annual rainfall may be of theorder of 600 mm, evaporative losses during the summer are typically ofthe order of 18 megaliter/hectare or a reduction in water depth of 1.8meters.

[0009] In more arid areas where average annual rainfall may be 200 mm orless, evaporative water losses of up to 30 megaliters/hectare have beenrecorded.

[0010] While the proportion of water lost by evaporation in waterstorage facilities can be reduced by increasing the depth/surface areratio, this is generally uneconomical.

[0011] For large capacity water storage dams of many hectares in surfacearea, these are usually constructed on flat land (without a surroundingcatchment area) by pushing up a perimetral wall of 2-3 meters in heightwith a bulldozer. It generally is not economically feasible to excavatelarge volumes of earth to form a water storage facility.

[0012] As far as the cost of evaporative losses are concerned, these maybe measured by the cost of water purchased and/or the value of lostagricultural production.

[0013] Typically, in an irrigation area where water is pumped from astream, the cost of a water allocation license may cost from $1000-$3000as an initial fee and a seasonal pumping cost of about $25 per megalitersubject to volumetric limits. These costs are steadily increasing aswater becomes scarcer due to seasonal variations and increased levels ofhorticulture.

[0014] If evaporative losses were to be measured in terms of lostagricultural production otherwise possible, the value per megaliter ofwater could range between $500 for a cotton crop up to $1000 or evenhigher for high value crops such as vegetables or the like.

[0015] Another problem associated with evaporative losses from openstorage ponds is the risk of increased salinity in water applied tocrops as water levels diminish due to evaporation. This problem can beexacerbated where the water is constantly held in storage i.e. thestorage pond is never completely emptied to remove accumulated saltconcentrations.

[0016] Over the years there has been extensive research into reductionof evaporative water losses.

[0017] Prior art proposals have included chemical, physical, andstructural methods.

[0018] Typically, chemical methods comprise the use of a chemicalmonolayer on the water surface to reduce the evaporation rate. The mostwell known of these is the use of cetyl alcohol.

[0019] While chemical monolayers have proven useful in pilot studies onsmall surface areas, there are real practical difficulties inmaintaining the integrity of the monolayer due to wind actions well ascontamination and biodegration of the monolayer.

[0020] Physical methods of evaporation control include destratificationto bring cooler water to the surface, however, this is of little valuein reducing evaporative losses due to wind action.

[0021] Other physical methods have involved floating covers made from:

[0022] expanded perlite ore

[0023] polystyrene beads

[0024] foamed wax blocks

[0025] white spheres

[0026] butyl rubber sheets painted white

[0027] polystyrene sheets and rafts

[0028] white foamed wax in continuous layers

[0029] foamed butyl rubber

[0030] light grey asphaltic concrete blocks.

[0031] While encouraging results have been obtained with some of thesesystems (up to 80% reduction with floating concrete rafts) none aresuited to very large water storages having a surface area of manyhectares due to cost.

[0032] Structural methods including roofing of reservoirs have shownevaporation reductions of up to 90% but again, the cost of suchstructures is not feasible for large surface areas.

SUMMARY OF INVENTION

[0033] Accordingly, the present invention seeks to overcome orameliorate at least some of the disadvantages of prior art waterevaporation reducing systems and to provide, if not a more costeffective system, at least a useful alternative choice.

[0034] According to one aspect of the invention, there is provided, asystem for reducing evaporation losses in a large surface area waterstorage, said system comprising: a buoyant flexible membrane extendingover a substantial portion of the surface of a body of water, saidmembrane being anchored by flexible anchoring means spaced about theperiphery thereof and connected to a peripheral wall of said waterstorage, said membrane characterized in that it comprises a plurality ofmembrane elements engageable along respective adjacent edges thereof,said membrane further characterized in the provision of spaced aperturesto prevent, in use, accumulation of rain water on an upper surfacethereof.

[0035] Suitably, the flexible membrane is comprised of a natural orsynthetic polymeric material.

[0036] If required, the flexible membrane may comprise a closed cellfoam structure for buoyancy.

[0037] Alternatively the flexible membrane may comprise spaced buoyancychambers.

[0038] Preferably the spaced buoyancy chambers extend over at least onesurface of said membrane.

[0039] Most preferably the buoyancy chambers extend over a surface ofsaid membrane, in use, in contact with the surface of the body of water.

[0040] The buoyancy chambers may be interconnected if required.

[0041] The membrane elements suitably comprise parallel sided membershaving telescopically engageable connection means extending adjacentopposed longitudinal edges.

[0042] Suitably the telescopically engageable connection means comprisesan elongate socket-like element extending adjacent one edge of saidmembrane element and an elongate spigot-like element extending adjacentan opposite edge, each said socket-like element and spigot-like elementbeing telescopically engageable in a respective complementary connectionmeans of an adjacent membrane element.

[0043] Alternatively the membrane elements may comprise connectionmembers spaced along opposite sides thereof. If required, the connectionmembers may comprise apertured eyelets, interengageable hooks and eyesor hooks and eyes engageable by a cord member.

[0044] The flexible anchoring means suitably comprises cord-like membersadapted for attachment to spaced anchor members located about theperipheral wall of said water storage.

[0045] According to another aspect of the invention there is provided amethod of reducing the evaporative losses in a water storage, saidmethod comprising the installation in a large surface area water storageof a system according to the first aspect of the invention.

BRIEF DESCRIPTION OF DRAWINGS

[0046] In order that the invention may be more readily understood andput into practical effect, reference is now made to a preferredembodiment illustrated in the accompanying drawings in which:

[0047] FIG 1 shows a water storage embodying a water evaporationreducing system according to the invention.

[0048]FIG. 2 shows schematically a method of installing the systemillustrated in FIG. 1.

[0049]FIG. 3 shows an enlarged cross-sectional view of thetelescopically interengageable connection means of the buoyant membrane.

[0050]FIG. 4 shows an alternative connection between adjacent membraneelements.

DETAILED DESCRIPTION

[0051] In FIG. 1 the water storage 1 comprises a raised earthen bank 2with a buoyant membrane 3 anchored to the earthen bank 2 by flexiblecords 4 secured at one end to the parallel sided membrane elements 5 bymeans of eyelets 5 or the like.

[0052] The other end of each cord 4 is secured to a peg 7 or othersuitable anchor in the bank 2.

[0053] The flexible cords may comprise some degree of elasticity toaccommodate movement of the membrane 3 as the water level rises or fallsthereunder. Generally speaking however it is considered that there issufficient resilience in the plastics or rubber membrane 3 to maintainsufficient tension in the cords 4.

[0054] If required, the membrane 3 may include one or more openings 8about its periphery to permit stock to drink or otherwise to accommodatean inlet or outlet conduit (not shown).

[0055]FIG. 2 shows one method of installing the system shown in FIG. 1.

[0056] A roll 10 of buoyant membrane material 11 of any suitable widthtypically from 3-5 meters or more is initially set up on a roll stand 12outside the earthen bank 13 of the water storage 14 and at one end 15thereof.

[0057] Using a rope or the like tied to the free end of the buoyantmembrane 11, the free end is drawn over the surface of the waterthereunder until the first roll 10 is nearly exhausted.

[0058] A second roll 16 of membrane material 11 is set up on a rollstand 17 behind the first roll 10 with a thermal welding device 18 suchas a radio frequency welder therebetween, the welder being powered by aportable electric generator 19.

[0059] The tail of first roll 10 is welded to the beginning of roll 16and the strip of membrane 11 is drawn across the surface of the waterwith further rolls of membrane material being added as required untilthe membrane strip reaches the opposite bank (not shown) of the waterstorage.

[0060] As an alternative, mechanical fastening means may be employed tojoin the ends of membranes 11.

[0061] Both ends of strip 11 and edge 11 a are secured to the bank 13 byflexible cords 20 connected to eyelets 20 along the side and ends of thesheet 11, the cords 20 being secured at their opposite ends to pegs orstakes 22 in the earthen bank 13.

[0062] Roll-stands 10 and 17 with associated rolls of buoyant material11 a, 16, together with the strip welder 18 are then aligned with thefree edge of the strip 11 floating on the surface of the water instorage 14.

[0063] An elongate spigot shaped telescopic connection means (not shown)along one side of new roll 11 is connected with an elongate socketshaped telescopic connection means (not shown) associated with anadjacent side of already installed strip 11 a.

[0064] By means of a rope 23, new strip 11 a in telescopic engagementwith adjacent strip 11, is drawn out over the surface of the water andthe process is continued until substantially the entire surface area ofthe water storage 14 is covered by a continuous buoyant membranecomprising membrane elements joined along adjacent edges.

[0065] Suitably cord 23 is passed around a pulley (not shown) on theopposite earthen bank to enable a one person operation and otherwise toprovide a free end of cord 23 for connection of a subsequent strip ofmembrane material.

[0066] The free ends of each strip are anchored progressively as theyare installed and the free edge of the last strip is also anchored afterinstallation to provide a secure integral barrier against evaporationdue to thermal and/or wind effects.

[0067] The simplicity of the apparatus needed for installation enablesease of installation in remote areas with a minimum of labour content inorder to minimize the cost/hectare of installation.

[0068] Over very large distances the friction between the telescopicallyengaging connection members may exceed the tensile strength of the stripof membrane and/or the connection member(s) under tensionnotwithstanding the presence of water as a lubricant.

[0069] In such circumstances a shorter panel may be drawn to the middleof the water storage from one side of the water storage and thereafteradditional short panels are drawn from the same side of the waterstorage to abut the previous panel. The process is then repeated fromthe opposite side of the water storage to form an effective cover overthe entire width of the water storage.

[0070]FIG. 3 shows schematically the telescopic connection betweenadjacent strips of buoyant membrane material.

[0071] Suitably the membrane 30 comprises a laminated thermoplasticsmaterial having a plurality of air filled buoyancy chambers 31 extendingfrom a lower surface.

[0072] Alternatively as shown by membrane 30 a, the buoyancy chambers 31a may comprise spaced transversely and/or longitudinally extending airfilled chambers.

[0073] Secured along opposing sides of the membrane are extruded members32, 33 in the form of elongate socket and spigot shaped telescopicallyengageable connection members.

[0074] The connection members 32, 33 may be secured to the membranesides by any suitable means such as stitching, adhesive material or bythermoplastic welding.

[0075] Located between the buoyancy chambers 31 (or 31 a) are apertures34 at spaced intervals. These apertures, in use, prevent ponding ofrainwater on the upper surface of the membrane which might otherwisecause the membrane to sink in parts and apply excessive tension in theanchoring means.

[0076] The clearance between the complementary socket and spigotconnectors is sufficiently great as to permit low friction telescopicengagement, particularly in the presence of water as a lubricant, butotherwise to maintain sufficient structural integrity to prevent beingpulled apart in high wind conditions.

[0077] By placing the protruding buoyancy chambers on the underside ofthe membrane, the contact area with the water is increased substantiallyto reduce the wind lift factor.

[0078] In addition by providing a relatively smooth upper surface to themembrane, collection of dust, leaves and other debris is minimized andthe smooth upper surface will be cleaned by rain and wind action.

[0079]FIG. 4 shows an alternative method of connecting adjacent membraneelements 40, 41.

[0080] As shown, elements 40, 41 comprise laminates of plastic filmhaving spaced buoyancy chambers 42 over at least a lower surface 43thereof.

[0081] Opposite side edge regions 44, 45 of the membrane elements may befree of buoyancy chambers and permit free overlapping of regions 44, 45.

[0082] A fastener 46 of a type similar to that used in the aircraftindustry for joining thin sheets of aluminum alloy or the like isinserted from one side (typically the top) of the overlapped region toform a pierced aperture 47 and the fastener 46 is then actuated by anactuating tool to cause finger-like elements 48 to frictionally engageagainst the underside of fastener 46 in the region of collar 49 tosecurely clamp the membrane elements 40, 41 together.

[0083] A suitable type of fastener may be a “BULBEX” type rivet-likefastener available from Textron Inc. or a similar fastener suitable forplastic sheets, with or without localized reinforcing e.g., washers.

[0084] Although the membrane may be comprised of any suitable polymericmaterial such as polyvinyl chloride, polyethylene butyl rubbers or anyother polymeric material having suitable mechanical and physicalproperties, the raw material costs and manufacturing methods for sheetlike membranes will mitigate against many of these polymers.

[0085] It is considered that “layflat” polyethylene film provides thebest compromise between cost and available film width.

[0086] Moreover, as film appearance is unimportant it is considered thatreclaimed polyethylene, pigmented black or white, with or without anappropriate ultra-violet light stabilizer will provide a cost effectivemembrane material with adequate resistance to weathering of between 2-5years before replacement becomes necessary.

[0087] To further reduce costs, it is considered that the buoyantmembranes according to the invention may be manufactured on site fromrolls of “layflat” polyethylene film and rolls of extruded socket andspigot telescopic connector means.

[0088] Layflat film up to 3 meters in width is available as a flattenedtube in rolls in excess of 100 meters.

[0089] A portable laminator could for example comprise say a 3 meterwide hollow drum having a pattern of perforations in its outer surfacein fluid communication with a vacuum pump.

[0090] As the double layer of film passes over a region of reducedinternal pressure in the drum, the lower layer of film is vacuum formedwith a plurality of hollow protrusions extending partly into the drumperforations.

[0091] An oil heated laminating roller then fuses the upper layer of thefilm to the lower layer thereby forming closed cell buoyancy chambers.

[0092] The 3 meters wide strips may then be welded together alongadjacent edges by a simple continuous thermal welding device to formmembrane elements of from say, 9-15 meters in width.

[0093] The extruded socket and spigot strips may be attached again by acontinuous thermal welding process in a separate step or as the membraneelements are drawn across the surface of the water during installation.

[0094] It will be readily apparent to a skilled addressee that manymodifications and variations may be made to the invention withoutdeparting from the spirit and scope thereof.

[0095] For example, instead of a telescopic engagement between adjacentstrips of membrane, the strips may be secured along adjacent edges bylacing or by any other suitable spaced mechanical connectors such asaligned eyelets, sheet material fasteners or the like, the connectionbeing effected from a small floating platform or boat moving between theedges of adjacent membrane strips.

[0096] In another embodiment each strip of membrane may be formed withapertured eyelets spaced along one longitudinal edge and transverselyaligned hook members spaced along an opposite edge.

[0097] Adjacent strips of membrane may then be connected by engaging theadjacent hooks and eyes of respective strips of membrane from a floatingplatform or alternatively by connecting a cord, laced through the spacedeyes along one edge of a strip of membrane, with hooks spaced along anadjacent edge of an adjacent strip of membrane.

[0098] Throughout this specification and claims which follow, unless thecontext requires otherwise, the word “comprise”, and variations such as“comprises” or “comprising”, will be understood to imply the inclusionof a stated integer or group of integers or steps but not the exclusionof any other integer or group of integers.

1. A system for reducing evaporation losses in a large surface areawater storage, said system comprising: a buoyant flexible membraneextending over a substantial portion of the surface of a body of water,said membrane being anchored by flexible anchoring members spaced aboutthe periphery thereof and connected to a peripheral wall of said waterstorage, said membrane characterized in that it comprises a plurality ofmembrane elements engageable along respective adjacent edges thereof,said membrane further characterized in the provision of spaced aperturesto prevent, in use, accumulation of rain water on an upper surfacethereof.
 2. A system as claimed in claim 1 wherein the flexible membraneis comprised of a natural or synthetic polymeric material.
 3. A systemas claimed in claim 2 wherein the flexible membrane comprises a closedcell foam structure for buoyancy.
 4. A system as claimed in claim 1wherein the flexible membrane comprises spaced buoyancy chambers.
 5. Asystem as claimed in claim 4 wherein the spaced buoyancy chambers extendover at least one surface of said membrane.
 6. A system as claimed inclaim 5 wherein the buoyancy chambers extend over a surface of saidmembrane, in use, in contact with the surface of the body of water.
 7. Asystem as claimed in claim 4 wherein the buoyancy chambers areinterconnected.
 8. A system as claimed in claim 1 wherein the membraneelements comprise parallel sided members having telescopicallyengageable connection means extending adjacent opposed longitudinaledges.
 9. A system as claimed in claim 8 wherein the telescopicallyengageable connection means comprises an elongate socket-like elementextending adjacent one edge of said membrane element and an elongatespigot-like element extending adjacent an opposite edge, each saidsocket-like element and spigot-like element being telescopicallyengageable in a respective complementary connection means of an adjacentmembrane element.
 10. A system a claimed in claim 1 wherein the membraneelements include connection members spaced along opposite sides thereof.11. A system as claimed in claim 10 wherein the connection memberscomprise apertured eyelets, interengageable hooks and eyes or hooks andeyes engageable by a cord member.
 12. A system as claimed in claim 10wherein the connection members are insertable from one side of anoverlapped region between adjacent membrane elements.
 13. A system asclaimed in claim 1 wherein the flexible anchoring members comprisescord-like members adapted for attachment to spaced anchors located aboutthe peripheral wall of said water storage.
 14. A method for reducingevaporative losses in a large surface area water storage, said methodcomprising the installation over the surface of a body of water in saidwater storage of a buoyant flexible membrane extending over asubstantial portion of a body of water, said membrane being anchored byflexible anchoring members spaced about the periphery thereof andconnected to a peripheral wall of said water storage, said membranecharacterized in that it comprises a plurality of membrane elementsengaged along respective adjacent edges thereof, said membrane furthercharacterized in the provision of spaced apertures to prevent, in use,accumulation of rainwater on an upper surface thereof.
 15. A method asclaimed in claim 13 wherein membrane elements are successfully extendedover the surface of said body of water and connected together atrespective adjacent edges thereof.
 16. A method as claimed in claim 14wherein said membrane elements are extended over the surface of saidbody of water by drawing a free end of a membrane element over thesurface of said body of water from one peripheral wall of said waterstorage to an opposite peripheral wall.
 17. A method as claimed in claim13 wherein adjacent membrane elements are engaged along respectiveadjacent edges thereof by overlapping said respective adjacent edges andinserting a connection member through said overlapping respectiveadjacent edges from one side thereof and actuating said connectionmember.